The present invention relates to surface treated electrodes particularly applicable to positive electrodes of zinc-halogen secondary batteries such as zinc-bromine secondary batteries and so on. The present invention particularly relates to the surface treated electrodes in which active carbon (activated charcoal) fibers whose originating raw materials are phenol formaldehydes are adhered onto conductive electrode substrates, for example, under mechanical pressure and heat or attached thereto.
Carbon fibers are effective materials as materials for surface treatments of positive electrodes in zinc-halogen secondary batteries. An electrode under a surface treatment has conventionally been used with such a carbon fiber as belonging to cloth-formed rayon and acryl series adhered onto a surface of a carbon plastic (C.P) under mechanical pressure and heat.
However, such carbon fibers as belonging to the rayon and acryl series in the above-described cloth forms have problems in their activation processing methods so that sufficient activations in zinc-halogen secondary batteries, especially in zinc-bromine secondary batteries cannot yet be achieved.
That is to say, since an area of a part occupied by pores having diameters of 1 to 11 nm required for a positive electrode reaction in the above-described electric secondary batteries is not yet formed in a sufficient quantity to carry out the positive electrode reaction in the above-described carbon fibers, an over voltage becomes remarkably large when the charge and discharge operations are carried out especially in high current densities equal to or more than 60 mA/cm.sup.2.
In addition, since the above-described carbon fibers have small weights per unit area in a unit of sheet (referred to as a METSUKE in Japanese and this unit is g/m.sup.2 in Japan and lb/yd.sup.2 in England), are thin in thickness, and weak in mechanical strength such as tensile and bending strengths, they cannot withstand a high mechanical pressure under which they are adhered onto the carbon plastics (C.P) by heat pressing operation, many such carbon fibers are destroyed to become powders and to become short length fibers during this process so that they drop off electrode surfaces. Consequently, electrochemical performances of the zinc-bromine secondary batteries will greatly be reduced.